| 1. |
- Grechnev, G. E., et al.
(författare)
-
Electronic structure and bulk properties of MB6 and MB12 borides
- 2008
-
Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 34:11, s. 921-929
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio band structure calculations are carried out for the higher borides MB6 and MB12. High-precision measurements of the elastic constants are performed for the compounds ZrB12, HoB12, ErB12, TmB12, LuB12, YB6 and LaB6 at low temperatures. The bulk properties of the borides are analyzed on the basis of the calculated equations of states and balanced crystal orbital overlap populations. Our calculations indicate that hexaborides with divalent metals, CaB6, SrB6, BaB6, and YbB6, are semiconductors with small energy gaps. The metallic MB6 hexaborides with trivalent M atoms are found to possess larger bulk moduli values. For dodecaborides the bulk moduli are found to be higher for MB12 with increased filling of the conduction band (ZrB12, HfB12, UB12) in comparison with M3+B12 compounds. The total energy calculations for different magnetic configurations in YbB12 point to the possibility of antiferromagnetic coupling between Yb3+ ions.
|
|
| 2. |
- Alimadadi, Hossein, 1983, et al.
(författare)
-
Corrosion properties of electrodeposited nanocrystalline and amorphous patterned Ni-W alloy
- 2009
-
Ingår i: MATERIALS & DESIGN. - : Elsevier BV. - 0261-3069 .- 0264-1275 .- 1873-4197. ; 30:4, s. 1356-1361
-
Tidskriftsartikel (refereegranskat)abstract
- Nickel-tungsten with satisfactory corrosion properties is a promising alloy to replace hard chromium. Relatively high adhesion between copper substrate and electrodeposited Ni-W alloy results in patterned morphology due to crack formation. In this work, corrosion resistance of patterned Ni-W alloys comprising 0-26 at.%.W were studied by potentiodynamic polarization and EIS in a medium containing Cl-. It is shown that corrosion resistance of single phase Ni-W is superior to amorphous and dual phase coated layers. It is also found that crack density is the dominant affecting factor on corrosion resistance of amorphous Ni-W alloys.
|
|
| 3. |
- Mikhaylushkin, Arkady S, et al.
(författare)
-
High-pressure structural behavior of large-void CoSn-type intermetallics: Experiments and first-principles calculations
- 2008
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : Institutionen för fysik, kemi och biologi. - 1098-0121 .- 1550-235X. ; 77:1, s. 014102-
-
Tidskriftsartikel (refereegranskat)abstract
- The high-pressure structural behavior of the binary intermetallic compounds CoSn, FeSn, and NiIn with the peculiar void containing CoSn (B35)-type structure has been studied by means of room-temperature diamond anvil cell and high-temperature multianvil experiments, as well as by first-principles calculations. All three compounds remain structurally stable at pressures up to at least 25 GPa, whereas first-principles calculations predict high-pressure structural changes below 20 GPa. A plausible explanation for the discrepancy is that at room temperature, a sizable activation barrier inhibits kinetically the transformation into more close-packed polymorphs. It is supported by our experiments at temperatures around 1000 °C and a pressure of 10 GPa. At these conditions, NiIn transforms into the temperature-quenchable stoichiometric CsCl-type high-pressure phase, which has been predicted in our first-principles calculations. However, CoSn and FeSn decompose into a mixture of compounds richer and poorer in tin, respectively. Nevertheless, it might be possible that lower temperatures and higher pressures may afford theoretically predicted polymorphs. In particular, a phase transformation to the FeSi-type structure predicted for CoSn is of interest as materials with the FeSi-type structure are known for unusual thermal and transport properties.
|
|
| 4. |
- Vitos, Levente, et al.
(författare)
-
Large magnetoelastic effects in paramagnetic stainless steels from first principles
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:2
-
Tidskriftsartikel (refereegranskat)abstract
- Using first-principles theories, we demonstrate that the elastic properties of substitutional disordered Fe-rich Fe-Cr-Ni alloys (austenitic stainless steels) sensitively depend on their magnetic state. Due to the strong magnetoelastic effects in paramagnetic Fe0.70Cr0.15Ni0.15 alloy, the room-temperature magnetism is found to alter the usually dominating chemical effects and give a large anomalous contribution to the temperature dependence of the elastic constants.
|
|
| 5. |
- Zha, Chaolin, et al.
(författare)
-
Pseudo spin valves based on L10 (111)-oriented FePt fixed layers with tilted anisotropy
- 2009
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate magnetoresistance (MR) in excess of 4% in FePt/CoFe/Cu/CoFe/NiFe pseudo spin valves based on L10 (111)-oriented FePt fixed layers with a 36 degrees out-of-plane tilted magnetization. The high MR is achieved by increasing the spin polarization at the Cu interfaces, using thin CoFe, and optimizing the FePt growth and Cu interface quality using Ta and Ta/Pt underlayers. We observe well-separated switching of the FePt/CoFe fixed layer and the CoFe/NiFe free layer, suggesting that CoFe is rigidly exchange coupled to FePt and NiFe in the respective layers.
|
|
| 6. |
- Gorbatov, O. I., et al.
(författare)
-
Effect of magnetism on precipitation of Cu in bcc Fe : Ab-initio based modeling
- 2009
-
Ingår i: Scientific basis for nuclear waste management XXXIII. - : Materials Research Society. - 9781605111667 ; , s. 469-476
-
Konferensbidrag (refereegranskat)abstract
- Theoretical modeling of the decomposition in bcc Fe-Cu alloys has been performed using a combined approach which includes ab-initio calculations of the effective cluster interactions and statistical-mechanical (Monte Carlo) simulations. We showed that the effective Cu-Cu and Cu-vacancy interactions in the bcc Fe matrix have a strong dependence on the global magnetic state of iron. As a result, all the related thermodynamic properties of the alloys (such as solubility limit and diffusivity) are expected to have a pronounced non-Arrhenius temperature behavior, originated from variation of the global magnetization with temperature. We find that strong Cu-vacancy interactions in the bcc Fe matrix lead to a remarkable effect of vacancies on the Cu precipitation and significantly modify the alloy decomposition kinetics under irradiation.
|
|
| 7. |
- Hu, Qing-Miao, et al.
(författare)
-
Site occupancy, magnetic moments, and elastic constants of off-stoichiometric Ni2MnGa from first-principles calculations
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:14
-
Tidskriftsartikel (refereegranskat)abstract
- The site occupancy and elastic modulus of off-stoichiometric Ni2MnGa alloys are investigated by the use of the first-principles exact muffin-tin orbital method in combination with coherent-potential approximation. The stable site occupancy at 300 K is determined by comparing the free energies of the alloys with different site-occupation configurations. It is shown that, for most of the off-stoichiometric Ni2MnGa, the "normal" site occupation is favorable, i.e., the excess atoms of the rich component occupy the sublattice(s) of the deficient one(s). Nevertheless, for the Ga-rich alloys, the excess Ga atoms have strong tendency to take the Mn sublattice no matter if Mn is deficient or not. Based on the determined site occupancy, the elastic moduli of the off-stoichiometric Ni2MnGa are calculated. We find that, in general, the bulk modulus increases with increasing e/a ratio (i.e., the number of valence electrons per atom). The shear moduli C-' and C-44 change oppositely with e/a ratio: C-' decreases but C-44 increases with increasing e/a. However, the Mn-rich Ga-deficient alloys deviate significantly from this general trend. The correlation of calculated elastic moduli and available experimental martensitic transformation temperatures (T-M) demonstrates that the alloy with larger C-' than that of the perfect Ni2MnGa generally possesses lower T-M except for Ni2Mn1+xGa1-x.
|
|
| 8. |
- Alling, Björn, et al.
(författare)
-
Effect of thermal expansion, electronic excitations, and disorder on the Curie temperature of Ni1-xCuxMnSb alloys
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:13
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the importance of thermal effects such as temperature-induced electronic, magnetic and vibrational excitations, as well as structural defects in the first-principles calculations of the magnetic critical temperature of complex alloys using half-Heusler Ni1-xCuxMnSb alloys as a case study. The thermal lattice expansion and one-electron excitations have been accounted for self-consistently in the Curie temperature calculations. In the Ni-rich region, electronic excitations, thermal expansion, and structural defects substantially decrease the calculated Curie temperature. At the same time, some defects are shown to increase T-C in Cu-rich samples.
|
|
| 9. |
- Dziekan, Thomas, et al.
(författare)
-
Influence of vanadium spin-polarization on the dissolution of hydrogen in vanadium
- 2009
-
Ingår i: PHYSICAL REVIEW B. - 1098-0121 .- 1550-235X. ; 79:1, s. 012402-
-
Tidskriftsartikel (refereegranskat)abstract
- Transition-metal (TM)/V superlattices (TM=Cr,Fe,Mo) show certain peculiarities under hydrogen uptake. Here we investigate the influence of an induced magnetization of the V layers on the hydrogen dissolution by means of first-principles calculations. We find that below a certain value for the magnetic moment of the V host the hydrogen solubility is slightly reduced, whereas for larger moments the hydrogen dissolution becomes favored. The actual position of this transition depends on the tetragonal distortion of the V layers.
|
|
| 10. |
- Mattesini, Maurizio, et al.
(författare)
-
Elastic properties and electrostructural correlations in ternary scandium-based cubic inverse perovskites : A first-principles study
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79, s. 125122-
-
Tidskriftsartikel (refereegranskat)abstract
- Wehave performed ab initio calculations for the cubic inverse-perovskite Sc3EN(E=Al,Ga,In) systems to study their electronic band-structures and elastic properties.In this study, we used the accurate augmented plane waveplus local orbital method to find the equilibrium structural parametersand to compute the full elastic tensors. The obtained single-crystalelastic constants were used to quantify the stiffness of theSc-based ternary nitrides and to appraise their mechanical stability. Thesite-projected density of states, Fermi surfaces, and the charge-density plotshave also been used to analyze the chemical bonding betweenthe Sc6N cluster and the surrounding metallic lattice of eitherAl, Ga, or In atoms. Our calculations show that Sc3GaNhas the largest covalent Sc-N bonding-type character with the highestYoung, shear, and bulk moduli. Compared with the other twoisoelectronic systems, it also behaves as the most brittle materialwith a relatively large elastic anisotropy.
|
|
